ABSTRACT
Nitric oxide synthase activity was measured in Langerhans islets isolated from control and streptozotocin diabetic rats. The activity of the enzyme was linear up to 150 mug of protein from control rats and was optimal at 0.1 muM calcium, when it was measured after 45 min of incubation at 37ºC in the presence of 200 muM arginine. Specific activity of the enzyme was 25 x 10(-4) nmol [3H] citrulline 45 min(-1) mg protein(-1). Streptozotocin diabetic rats exhibited less enzyme activity both in total pancreas homogenate and in isolated Langerhans islets when compared to control animals. Nitric oxide synthase activity measured in control and diabetic rats 15 days after the last streptozotocin injection in the second group of animals corresponded only to a constitutive enzyme since it was not inhibited by aminoguanidine in any of the mentioned groups. Hyperglycemia in diabetic rats may be the consequence of impaired insulin release caused at least in part by reduced positive modulation mediated by constitutive nitric oxide synthase activity, which was dramatically reduced in islets severely damaged after streptozotocin treatment.
Subject(s)
Animals , Male , Rats , Diabetes Mellitus, Experimental/metabolism , Islets of Langerhans/enzymology , Nitric Oxide Synthase/metabolism , Analysis of Variance , Anti-Bacterial Agents , Rats, Wistar , StreptozocinSubject(s)
Humans , Animals , gamma-Aminobutyric Acid/metabolism , Glutamate Decarboxylase/metabolism , Islets of Langerhans/enzymology , Amino Acid Sequence , Autoantigens , Base Sequence , Central Nervous System/chemistry , Citric Acid Cycle , Glutamate Decarboxylase/analysis , Glutamate Decarboxylase/immunology , Molecular Sequence DataABSTRACT
Se describe un procedimiento simple que permite determinar la actividad de Ca2+ -ATPasa de membrana plasmática en homogenados de islotes de rata, empleando un medio con concentraciones bajas de Ca2+ y Mg2+ desprovisto de K+. La actividad de Ca2+ -ATPasa detectada es inhibida con alta afinidad por el vanadato y el compuesto 48/80 (droga con efecto anticalmodulina específico). La enzima presenta dos componentes para el Ca2+, uno con afinidad aparente alta y velocidad máxima baja y otro con afinidad aparente baja y velocidad máxima alta. Los valores obtenidos para estos dos componentes en hemogenados de islotes y en preparados de membranas parcialmente purificadas son similares. Estos resultados sugieren que la actividad Ca2+ -ATPasa detectada en los homogenados de islotes es la correspondiente a la membrana plasmática. Los islotes obtenidos de ratas sometidad a un ayuno de 48 h tuvieron una menor respuesta secretora a la glucosa y una disminución simultánea en la actividad de su Ca2+ -ATPasa. Estos resultados sugieren que la Ca2+ -ATPasa de la membrana plasmática de los islotes pancreáticos participaría en la regulación de la secreción de insulina (U)